1. Field of the Invention
The present invention relates to a master cylinder for use in a hydraulic brake apparatus of a vehicle, and more particularly to a master cylinder with a braking stroke simulator operated in response to operation of a manually operated braking member.
2. Description of the Related Arts
Heretofore, there is known various hydraulic brake apparatuses each having a master cylinder with a braking stroke simulator. Among them, such an apparatus as discussed below has been disclosed in Japanese Patent Laid-open publication No. 11-59349. According to the apparatus, when a pressure control device including a pressure source is normal, the hydraulic pressure generated by the pressure source is controlled by the pressure control device in response to operation of a manually operated braking member to be supplied into wheel brake cylinders, with the communication between the master cylinder and the wheel brake cylinder being blocked. When the pressure control device has come to be abnormal, the master cylinder is communicated with the wheel brake cylinder, to discharge the hydraulic pressure into the wheel brake cylinder in response to operational force of the manually operated braking member.
According to the hydraulic brake apparatus as described above, the stroke simulator is adapted to provide the manually operated braking member with a stroke in response to the braking operation force, when the pressure control device is normal, i.e., when the communication between the master cylinder and the wheel brake cylinder has been blocked. And, according to the hydraulic brake apparatus as disclosed in the Japanese Patent Laid-open publication, the stroke simulator is disposed between the manually operated braking member and a master piston. In view of the fact that it is required to provide a large stroke of a brake pedal in response to a stroke of the stroke simulator, when the pressure control device is abnormal, i.e., when the hydraulic pressure is supplied from the master cylinder to the wheel brake cylinder, there is provided a seal member which serves as cut-off means for blocking the communication between a simulator chamber and an atmospheric pressure chamber in response to movement of the master piston. With the seal member acting as the cut-off means properly, the stroke of the stroke simulator may be restricted, when the hydraulic pressure is supplied from the master cylinder to the wheel brake cylinder.
According to the hydraulic brake apparatus as disclosed in the Japanese Patent Laid-open publication, however, even if the seal member could not act as the cut-off means sufficiently, any abnormality could not be detected as far as the pressure control device is normal. Therefore, it is required to provide the manually operated braking member with a large stroke, when the pressure control device is abnormal. In view of reliability of the seal member acting as the cut-off means, a further improvement is required. As the stroke simulator is disposed behind the master piston according to the apparatus as disclosed in the Japanese Patent Laid-open publication, the longitudinal length of the master cylinder is made long, so that it is insufficient to fulfill the requirement for minimizing the master cylinder as a whole.